The present invention generally relates to extrusion processes and apparatuses therefor. More specifically, the present invention is concerned with processes and apparatuses for extruding chemical functional additives used in making disposable items, such as paper toweling, napkins, toilet tissue, facial tissue, etc.
Extrusion dies for depositing an extrudable fluid onto a substrate are known in the art. Dies of a type generally known in the art as a coat-hanger die are described, for example, in the following U. S. patents: U.S. Pat. No. 4,043,739 issued on Aug. 23, 1997 to Appel and assigned to Kimberly-Clark Corporation; U.S. Pat. No. 4,372,739 issued on Feb. 8, 1983 to Vetter et al. and assigned to Rxc3x6m GmbH of Darmstadt, Germany; U.S. Pat. No. 5,234,330 issued on Aug. 10, 1993 to Billow et al. and assigned to Eastman Kodak Company; U.S. Pat. No. 5,494,429 issued on Feb. 27, 1996 to Wilson et al. and assigned to Extrusion Dies, Inc. Several other types of extrusion apparatuses are disclosed, for example, in the following U.S. patents: U.S. Pat. No. 5,607,726 issued on March 1997 to Flattery et al. and assigned to E. D. du Pont de Nemours and Company; U.S. Pat. No. 5,522,931 issued to Iwashita et al. on Jun. 4, 1996 and assigned to Konica Corporation of Japan; U.S. Pat. No. 5,740,963 issued to Riney on Apr. 21, 1998 and assigned to Nordson Corporation; U.S. Pat. No. 5,511,962 issued to Lippert and assigned to Extrusion Dies, Inc.
One of the concerns relating to extrusion dies of prior art has been plugging of a die""s discharge mouth, i. e., the outlet through which the extrudable fluid exits the extrusion die. Extrusion dies are frequently used in dusty environments. In papermaking, for example, some paper webs tend to be particularly prone to release surface fibers. A dust comprising primarily papermaking fibers may cause contamination of a chemical functional additive, such as, for example, a topical tissue softener, which is routinely deposited onto the paper web. Other common contaminants may include degradation products of the extrudable fluid itself, which particularly may occur in stagnant areas around the walls of the extrusion die. Build up of these degradation products can form over a period of time, harden and eventually separate from the walls of the die, thereby becoming a contaminant. More generally, particulate soil, sand, dirt, and grit tend to become airborne in the vicinity of the extrusion operation and settle into the supply of the extrudable fluid feeding the extrusion die.
If the chemical functional softener, for example, is deposited onto a substrate by extrusion, the contaminants, which have found their way into the functional additive being extruded, may plug the discharge outlet of the extrusion die. A process of cleaning of the extrusion dies is usually costly, for it involves stoppage of a production line and/or a substantial effort. The cleaning may be further complicated in extrusion dies designed to extrude very thin layers of extrudates and therefore comprising the discharge mouths having very small (in the range of 0.0002-0.00450 inches) dimensions requiring maintenance of high-precision tolerances.
Now it has been found that the discharge mouth having a divergently xe2x80x9cflaredxe2x80x9d shape on a cross-section can beneficially mitigate, and even eliminate the problem of plugging of the discharge mouth. Accordingly, the present invention advantageously provides a novel extrusion apparatus comprising a discharge mouth having an entry open area and an exit open area which is greater than the entry orifice. The present invention also provides an advantage of an extrusion process which substantially eliminates plugging of the discharge mouth of the extrusion apparatus.
Other objects, features, and advantages of the present invention will be readily apparent from the following description taken in conjunction with accompanying drawings, although variations and permutations may be had without departing from the spirit and scope of the disclosure.
The present invention provides an extrusion die and a process for extruding an extrudable fluid onto a web substrate. A preferred extrudable fluid comprises a chemical functional additive commonly used in making consumer disposable articles, such as such as paper toweling, napkins, toilet tissue, facial tissue, sanitary napkins, diapers, etc. The extrudable fluid may be selected from the group consisting of softeners, emulsions, emollients, lotions, topical medicines, soaps, anti-microbial and anti-bacterial agents, moisturizers, coatings, inks and dies, and binders. A preferred web substrate comprises a fibrous web, such as, for example, a paper web. It is to be understood, however, that the extrusion die and the process of the present invention may be beneficially used with other types of the extrudable fluids and other types of the substrates.
An extrusion die of the present invention comprises a supply port and a distribution channel in fluid communication with the supply port. The distribution channel terminates with at least one discharge mouth having a passage cross-section therethrough. The discharge mouth comprises an entry orifice, an exit orifice, and a discharge distance therebetween. The entry orifice has an entry open area Ae, and the exit orifice has an exit open area Ax. According to the present invention, the exit open area Ax is greater than the entry open area Ae. A ratio Ax/Ae is preferably between about 1.1 and about 10, more preferably between about 1.2 and about 5, and most preferably between about 1.5 and about 2.
In a preferred embodiment of the extrusion die, the passage cross-section of the discharge mouth continuously and gradually increases from the entry open area Ae to the exit open area Ax. The discharge mouth is flared, preferably gradually and continuously, in at least one cross-section. More preferably, the discharge mouth is flared in at least two mutually perpendicular cross-sections, and most preferably, the discharge mouth is gradually and continuously flared in any of its cross-sections, i. e., around 360xc2x0 . The discharge mouth may have various configurations, including but not limited to: an elongate slot, a substantially circular aperture, and any combination thereof.
The discharge distance of the discharge mouth is preferably from about 0.0075 to about 0.1 inches, and more preferably from about 0.010 to about 0.050 inches. The exit open area Ax of the discharge mouth is preferably from about 0.10 to about 2.5 square inches, and more preferably from about 0.2 to about 1.0 square inches.
In the preferred embodiment, the extrusion apparatus further has a knife-edge lip. The discharge mouth(s) are associated with the lip such that during the process of extruding the web substrate may contact the edge-knife lip. In a particularly preferred embodiment of the extrusion die comprising a plurality of the circular discharge mouths, the edge-knife lip extends between the exit orifices of the discharge mouths. Such discharge mouths can be formed by drilling flared holes in the die through the edge-knife lip.
The process of the present invention comprises the following steps: providing an extrudable fluid; providing a web substrate; providing an extrusion die of the present invention described herein above; extruding the extrudable fluid through the discharge mouth of the extrusion die, while continuously moving the web substrate relative to the extrusion die; and contacting the web substrate with the extrudate. During the process, at least some of relatively large contaminants contained in the extrudable fluid, i. e., those contaminants that have at least one dimension which is greater than at least one dimension of the entry open area, are precluded from entering the discharge mouth. At the same time, at least some of relatively small contaminants, i. e., the contaminants having at least one dimension which is less than at least one dimension of the entry open area, pass through the discharge mouth without being obstructed therein. It is believed that during the described process using the extrusion die of the present invention, plugging of the discharge mouth is substantially reduced or even avoided.
Some of the contaminants that are precluded from entering the discharge mouth may still be disposed in the proximity of the entry orifice, thereby restricting flow of the extrudable fluid through the discharge moth. To avoid this problem, a back-pressure may, for a short period of time, be applied to the extrudable fluid inside the distribution channel.